Organic light emitting display devices draw lots of attention due to their advantages such as low power consumption, high brightness, low cost, wide angle of view, fast response, and so on, and have been widely used in the technical field of organic light emitting.
The Organic Light Emitting Diode (OLED) is a kind of light emitting device that is currently used a lot in the field of organic light emitting. Currently, OLEDs can be classified into two categories which are passive driving OLEDs and active driving OLEDs, i.e. direct addressing OLEDs and Thin Film Transistor (TFT) matrix addressing OLEDs. The active driving OLED is also referred to an Active Matrix OLED (AMOLED). The light emitting device in each sub-pixel unit is driven by a pixel circuit and a power line applying a direct current (DC) power voltage signal (VDD or VSS) to emit light.
Refer to FIG. 1 which is a schematic structural diagram of a pixel circuit for driving the light emitting device to emit light in the prior art, taking n type driving transistors as an example, the pixel circuit comprises a driving transistor T1, a capacitor C1 and a switch transistor T2.
A first terminal of the capacitor C1 is connected to the gate of the driving transistor T1, and a second terminal of the capacitor C1 is connected to a low level reference voltage source VSS. The drain of the switch transistor T2 is connected to the gate of the driving transistor T1, the gate of the switch transistor T2 is connected to a gate signal source VScan, and the source of the switch transistor T2 is connected to a data signal source VData. The source of the driving transistor T1 is connected to a high level reference voltage source VDD, the drain of the driving transistor T1 is connected to the anode of a light emitting device D1, and the cathode of the light emitting device D1 is connected to the low level reference voltage source VSS.
At the stage of displaying one frame of picture, before the light emitting device D1 is driven to emit light, the gate signal source outputs a voltage signal VScan to turn on the switch transistor T2, the data signal source is connected to the branch where the capacitor C1 is located, and the data signal source outputs a data signal VData to be applied to the second terminal of the capacitor C1 to charge the capacitor C1. At the stage of driving the light emitting device D1 to emit light, the capacitor C1 discharges to drive the light emitting device D1 to emit light.
The pixel circuit shown in FIG. 1 can only drive one light emitting device to emit light, and each light emitting device is corresponding to the light emitting area of one pixel unit. When scanning each frame of picture, signals all need to be written into the pixel circuit. When scanning each frame of picture, the light emitting areas corresponding to the pixel units all need to emit light for displaying. The driving mode in which the AMOLED display drives the OLED to emit light is DC driving. The electric field corresponding to a long time DC driving voltage would polarize the ions inside the OLED to make the OLED form a built-in electric field, such as to increase the threshold voltage of the OLED, decrease the light-emitting efficiency of the OLED dramatically, and shorten the lifetime of the OLED. The lifetime is an important factor limiting the wide application of the organic light-emitting display, in particular, the large size and high brightness organic light emitting display apparatus.